1. Field of the Invention
The present invention relates to a drive unit applicable to a copying machine.
2. Description of the Related Art
In the case of electronic copying machines, for example, particles of developing agent remaining on the surface of a photoconductive drum are scraped off by means of a cleaning blade after the developing and transfer processes have been completed. The blade is made to engage with the surface of the drum at the start of a copying operation, and is disengaged therefrom upon completion of the copying process.
When the copying operation is finished, the blade is disengaged from the photoconductive drum. The drum does not stop at once, continuing t rotate on its own inertia. Therefore, some developer particles remaining on the surface of the drum may carried past the point where the blade will contact at the start of the next copying operation. These residual particles cannot be removed by the blade during the next copying operation, and will inevitably form black stripes on a copy image, thus lowering the quality of the copy image.
To avoid this problem, the photoconductive drum is reversely rotated through a predetermined angle after the cleaning blade has been disengaged from the drum at the end of the copying operation. At the start of the next copying operation, the blade is brought into contact with the cleaned portion of the surface of the drum. Therefore, in the next copying operation, the blade sweeps that portion of the surface of the drum on which the developer particles remain, thus removing the residual particles from the drum.
In the conventional electronic copying machines, the developing rollers, fixing rollers, or the like, are driven simultaneously by the motor used to drive the photoconductive drum. The inertia of each of these rollers acts on the drum. As a result, it is difficult to stop the reversely rotating drum in a predetermined position.
The inside of the electronic copying machines must be cooled not only during the copying operation, but also during a standby period. A motor and a fan coupled to the motor are used exclusively during the standby period to cool the inside of the machines. Both the motor and the fan are relatively expensive components. Hence, in order to reduce the cost of the machines, it is desired that the inside of the machines be cooled during the standby period, without using such a motor and a fan.